The invention relates to image processors in general and in particular to image processors utilizing a rotating lead screw for moving a printhead. More particularly, the invention relates to an improvement in the performance, quality and cost of such a lead screw assembly. Still more particularly, the invention relates to an improved lead screw assembly that substantially minimizes shifting or movement.
Pre-press color proofing is a procedure long used by the printing industry for creating representative images of printed materials in an effort to lessen the high cost and time required to produce printing plates and to set up a high-speed, high volume, printing presses.
One such commercially available image processor, as depicted in U.S. Pat. No. 5,268,708, includes half-tone capabilities. Such printing systems are able to form an image on a sheet of thermal print media (TPM) in which dye from a sheet of donor material is transferred to the TPM by applying an adequate amount of thermal energy to the dye material. Generally, the processor is comprised of a material supply carousel and a lathe bed engine writing system. The write engine itself includes an engine frame, translation drive, translation stage member, write-head, image drum and exit port for the TPM and the dye donor sheets.
In operation, sheets of TPM and dye donor material are transported from the materials carousel and peripherally wrapped around the imaging drum. Once secured, a print engine provides the printing function by exposing the TPM and dye donor material while it rotated past the printhead by means of the rotating imaging drum. The translation drive then traverses the printhead is fixed onto a translation member, axially along the axis of the image drum and in a coordinated motion with the spinning drum. Inevitably, these movements combine to produce the intended image on the thermal print media. The processor repeats these step over again but with different colored dye donor sheets in order to produce the desired image. Once complete, both the TPM and the dye donor sheets are removed from the image drum and transported to their respective external holding trays.
To allow for movement of the printhead along the imaging drum, the translation stage with the printhead mounted thereon may be coupled to a lead screw nut which in turn is attached to a lead screw having a threaded shaft. An example of such a lead screw assembly is described and disclosed in U.S. Pat. No. 5,771,059, the entirety of which is incorporated herein by reference. The lead screw rests between the two sides of the write engine frame and is supported by a ball and bearing socket and a radial bearing at the drive end. The drive end of the lead screw continues through the radial bearing and is connected to the drive motor that provides rotation of the lead screw.
A problem associated with such lead screw assemblies is the tolerance between the lead screw and the bearing socket in which it fits. An increased tolerance between the end of the lead screw, which is usually a ball, and the mounting socket could result in the ball releasing from the mounting socket. Alternatively, the epoxy holding the ball in the mounting socket, if assembled improperly, can stick on the ball causing interference with the bearing pocket. This may lead to unwanted axial lateral shifting or movement of the lead screw assembly resulting in an image defect. Other problems include improper seating within the mounting socket or loss of the bond holding the lead screw within the mounting socket.
Accordingly, a need exists for an improved lead screw assembly that eliminates the problems associated with shifting or movement of the lead screw.
It is the object of the present invention to provide an improved lead screw assembly.
Another object of the present invention is to provide a ball end lead screw assembly that overcomes one or more of the problems set forth above.
Still another object of the present invention is to provide a lead screw assembly that eliminates shifting or movement of the lead screw within the write engine.
As such, disclosed in one embodiment is an improved lead screw assembly. The lead screw assembly comprises a threaded shaft having a ball end and a first member attached to the ball end. A second member is arranged to be magnetically attracted to the first member and spaced apart from the first member so as to prevent mechanical friction between the first and second members. The first and second members prevent substantial axial movement, shatter, or vibration of the threaded shaft while it rotates.
The lead screw assembly may further comprise a write engine frame adapted for housing the threaded shaft such that the shaft is firmly secured as it rotates. A motor is mounted on the engine frame, the motor having an output shaft attached to the opposite end of the threaded shaft and adapted for rotating the threaded shaft.
The first member may comprise a magnet mounted and attached to the ball end such that the ball end is annularly surrounded by the first member. Also, an end cap may be attached to the frame such that the cap provides an axial-stop for the lead screw. In one embodiment, the end cap comprises a circular flat surface and a shaped circular surface opposite the flat surface such that the shaped circular surface is adapted for receiving the ball end of the shaft and eliminate axial movement the shaft as it rotates.
Further disclosed is a print engine system having an improved lead screw assembly for improving an image generating process. The system comprises a print head and a lead screw nut coupled to the print head by means of a translation stage. A threaded shaft is insertably coupled to the lead screw nut and adapted to cause the lead screw nut to move the print head mounted on the translation stage axially along the threaded shaft. The print head is substantially stabilized as the nut moves axially along the shaft while the print head generates an image.
The system may also comprises a write engine frame adapted for housing the threaded shaft such that the shaft is firmly secured as it rotates. If so configured, a motor is provide and is mounted on the engine frame, the motor having an output shaft attached to the opposite end of the threaded shaft. The motor is adapted for rotating the threaded shaft.
The threaded shaft may further comprise a ball end and a first member mounted to and attached to the ball end. A second member is magnetically attracted to the first member and spaced apart from the first member so as to prevent mechanical friction between the first and second members while the shaft rotates.
According to one embodiment, the second member may further comprise an end cap attached to the write engine frame for providing an axial stop for the thread shaft. The end cap may further comprise a circular flat surface and a shaped circular surface opposite the flat surface. The shaped surface is adapted for receiving the ball end of the shaft so as to substantially diminish the axial movement of the shaft as it rotates.
The invention can be used in any image processing apparatus that uses thermal print media and dye donor materials or other similar materials using colorant.
An advantage of the present invention is that it simplifies the manufacture the lead screw assembly.
Another advantage of the present invention that it provides a better quality lead screw assembly.
Still another advantage of the present invention that it provides a lower cost lead screw assembly.
Although not described in detail, it would be obvious to someone skilled in the art that this invention could be used in other imaging applications where a lead screw is used for printhead positioning.